Fuse construction



lnited States Patent O FUSE CONSTRUCTION Leonard N. Baenziger, Pawtucket, R. I., assignor, by mesne assignments, to Royal Electric Corporation, Pawtucket, R. I., a corporation of Delaware Application April 18, 1955, Serial No. 501,870 11 Claims. (Cl. 200-123) The present invention relates to a novel construction for a circuit protective fuse. The type of fuse to which this invention particularly relates is one which is adapted not only immediately to protect the circuit in which it is connected from extreme current overloads, such as might be caused by a short circuit or the like, but also to protect the circuit against minor overloads which persist beyond a predetermined period of time.

Fuses of this particular type generally comprise a conductive link formed of readily fusible material, the link itself therefore being self-destructive so as to open the circuit through the fuse quite promptly upon the occurrence of heavy overloads. A portion of the electrical circuit through the fuse is additionally defined by a material having a fairly low melting point, that material serving to physically and electrically connect two elements together and being held under tension in juxtaposition to a current carrying element having an appreciable electrical resistance. Slight overloads will cause the element of high electrical resistance to heat up sufliciently to melt or soften the connecting material, and because of the tension thereon the junction defined thereby will separate provided that the heating effect of the high resistive element continues at a sufficient magnitude for a suflicient period of time. in this manner if a slight overload should occur the circuit through the fuse will not be immediately opened, but if that slight overload should continue for an excessive period of time, the circuit will be opened. The period of time will of course vary dependent upon the magnitude of the overload, the greater the current the greater the heat developed in the element having a high electrical resistance, and consequently the sooner will the junction material be softened or melted.

The fuse structure of the present invention provides for a simplified yet positively acting arrangement of parts in a device of this character. in particular the element of appreciable electrical resistivity which exerts a heating effect is in the form of a strip or bar connected at its ends to conductive elements, the connection at one, and preferably both, of its ends being constituted by material having a low softening point maintained under tension so as to facilitate a separation of the bar or strip from the appropriate conductive element when a moderate overload persists for an excessive period of time. At least one of the elements to which the bar is connected is formed of fusible material adapted to function promptly upon the existence of an excessive overload so as itself to open the circuit to the fuse. The arrangement is such that the Same spring which tensions the joint of low softening point also tends to keep said fusible element tensioned, thus ensuring its prompt and effective functioning upon the occurrence of an excessive overload. The arrangement of parts is simplified when compared With comparable structures of the prior art so as to facilitate manufacture and assembly and reduce cost. ferred that the heating effect be exerted at two separated circuit through either of those points being effective to interrupt current through the fuse, thus producing a greater degree of reliability.

To the accomplishment of the above, and to such other objects as may hereinafter appear, the present invention relates to a fuse construction as called for in the appended claims and as described in this specification, taken together with the accompanying drawings, in which:

Fig. l is a cross sectional View of the fuse made according to the present invention;

Fig. 2 is a View similar to Fig. l but showing the manner in which the fuse functions on the occasion of an excessive overload; and

Fig. 3 is a view similar to Fig. l but showing the manner in which the fuse functions when a moderate overload persists for an excessive period of time.

The fuse comprises a base plug 2 formed of a suitable insulative heat resistive material such as a ceramic or synthetic plastic and a body generally designated 4 also formed of an insulative material such as glass. The base plug 2 is provided with a flange 6 from which a sleeve 8 extends upwardly, the lower portion of the base 2 being tapered and terminating in a bottom surface 10 within which a recess l2 is formed, the recess 12 communicating with a passageway 1f:- which leads into the space 16 inside the sleeve 8. ri`he body 4 has a depending annular skirt 18 adapted to rest On the upper surface 2G of the flange 6, a bead 22 being formed on the outer surface thereof so as to dene a scre thread. A correspondingly threaded shell 24 of conductive material engages with the bead 22 and is provided with a lower inwardly extending lip 26 which engages the undersurface 28 of the base flange 6, thus holding the base 2 and the body 4 in assembled condition. The shell 24 defines one of the exposed terminals of the fuse and also constitutes the means by which the fuse may be screwed into the socket adapted to receive it.

The other external terminal of the fuse, located as is conventional in the lower tip thereof, is defined by a button 30 formed of any appropriate conductive material, that button being received in the base recess 12 and having a flange 32 integral therewith and projecting up therefrom through the passage 14, the upper end of the flange 32 being adapted to be spun over at 34 so as to rest upon an appropriately inclined inner surface of the base 2, thus serving to retain the button 3i) in place. A pair of fusible link sections 36 and 33 are employed. One end of the link section 36 extends upwardly along the outer surface of the body skirt 18, the bead 22 being interrupted to permit the link end to extend thereabove, said link end being connected to the shell 24 by means of solder 40. The other end of the link section 36 extends up along the inner surface of the body skirt 18 and then is bent over, at 42, so as to extend over the upper surface 44 of the base sleeve 8, an insulating washer li preferably being interposed therebetween.

The lower end of the link section 33 is connected to the central terminal button 3G by means of solder 4S, and its upper end extends through a notch 50 in the washer 46, its tip being bent over the upper surface of the washer 46 at 52.

A strip or bar 54 of material having an appreciable extends over and between the fusible link portions 42 and 52 and is secured to those portions by means of solder or the like 56, 56 having a comparatively low softening or melting point.

A spring 58, here shown as of the coiled compression type, is mounted between the undersurface of the washer 46 and the bottom of the opening 16 in the base 2, the lower end of the spring 58 being here specifically shown as resting on an insulated washer 60 provided with a notch 62 through which the link section 16 extends. but` that tendency is prevented by means of the solder 56 which connects the link section 38 with the resistive rod o r bar 54.. Consequently the link section 3S, at least above the washer 6i), is also maintained under ten-Y sion by the spring 53. A suitable portieriY or portions of vthe tensioned part of the link section 38 may be weakened or narrowed in conventional manner.

Upon the occurrence of an extreme overload the link sections 36 and 33 will tend to fuse or melt. This fusing will take place iirst at any weakened portions thereof. Consequently, as @may be Seen in Fig. 2, the link section 38 will fuse or melt at some point on the tensioned length thereof which has previously been weakened, the

spring 55u/ill expand, the washer d6 will be lifted, and thatr port-ion` of the link ksection 3S above the weakened area will be separated from the portion thereof below the weakened area, thus positively and quickly opening the circuit through the 'fuse and interrupting the current there- Y through. Of course, if some portion of the link section` 36-should fuse, the spring 5S, acting through the washer 46, would cause that link section to separate appreciably in substantially the same manner as has just been described.

In the event that a moderate overload should occur of a magnitude insufficient to cause either of the links 3:6Y or 38 to fuse or melt, the current in passing through the rod or bar ft-'will cause an abnormal amount of heat to be produced therein in accordance with well known electrical laws. ri`his heat will be transmitted to the low softening point solder 56, 56'. That solder constitutes the only mediu-m connecting the rod or bar 54 to the link ends 42 or 52. The spring 5S, in tending to urge Vthe washer 46 upwardly, maintains the solder 56 and 56' under tension, constantly tending to separate the link ends 42 and 52 therefrom. if the solder 56 or 56 should soften sufliciently, as will be the case if suflicient heat is applied thereto for a sufficient period of time, the aforementioned tendency of the spring 58 will become an actuality, as illustrated in Fig. 3, and the washer 45 together with the rod or bar 54 will be lifted While the link sections 36A and 3S will remain in place. As a result the, connection between the rod or bar 54 and one or both ofthe. link section ends 42 and 52 will be broken, and

the current through the fuse will be interrupted. Fig. 3 discloses the condition of the fuse when both of the solder jointsS and 56 have failed because of softening. Howeveu, ifonly'one of the joint 56 or 56 should fail current Y through the fuse will nevertheless be interrupted', the

washer 46 then being lifted in an inclined manner such asshown in Fig. 2.

it will be seen from the abovethat the construction in question is extremely sturdyv and simple, and that the fuse parts may be very readily assembled. A single spring not only tensions a link section which is adapted to fuse upon the existence of a moderate overload for an excessive period of time. Thus reliability of action is ensured in an extremely simple and inexpensive manner.

While-but a single embodiment of theV present invention has been here disclosed, it will be apparent that many variations may be made therein, all within the spirit of the present invention as defined in the following claims.

l claim:

l. A fuse construction comprising a hollow housing having first and second tenminals exposed at the exterior the cof, apair of link sections, at least one-.being fusible, each ofl said sections being connected toa different terminaland extending into saidl housing to separated points, a connecting bar of material having a comparatively high resistance electrically connected tosaid link sections at said points and connected to oneof. said link-sections by Vnlaterial haying'a'low melting point, and resilientY means insaickhousing active on said-bar ina/directionV subsilmialy perpendicu'lar.v to` its length to urge itY away The spring 58 thus tends to lift the washer 46 Y from said one of said link sections, thereby tensioning the connection between it and saidv one of said link sections.

2. A fuse construction comprising a hollow housing having iirst and second terminal exposed at the exterior thereof, a pair of link sections, each of said sections being connected to a diferent terminal and extending into said housing to separated points, a connecting bar of material having a comparatively high resistance electrically connected to said link sections at said points and connected to one of said link sections by material low melting point, and resilient means in said housing active on said bar in a direction substantially perpendicular to its length to urge it away from said one of said link sections, thereby tensioning the connection between it and said one of said link sections, said one of said link sections being fusible.

3. A fuse construction comprising a hollow housing having first and second terminals exposed at the exterior thereof, a pairv of link sections, each of said sections being connected to a different terminal and extending to said housing to separated points, a connecting bar ofY material having a comparatively high resistance electrically connected to said linkV sections at said points and connected toone of said link sections by material having a low melting point, and resilient means in said housing active on said bar to urge it away from said one of said link sections, thereby tensioning the connection between it and said one of said link sections, said one of said link sections being fusible, said means being active in a direction substantially parallel to the direction in which said one of said link sections extends from the terminal to which it is. connected, thereby tensioning said link section as4 well', said bar extending from said one of said link sections in a direction substantially perpendicular thereto. v 4. A fuse construction comprising a hollow housing having first and second terminals exposed at the exterior' thereof, said rst terminal being at the bottom of said housing and said second terminal being at the side thereof, a pair of link sections, one connected to said first terminal and extending up into said housing, the other connected to saidsecond terminal and extending into said housing toa point spaced laterally from the end of said onelink section, said one link sectionV being fusible., a connecting bar of material having a comparatively high resistance extending substantially laterally across said housing, electrically connected to the ends of said link sections and connected tothe end of said one link section by material having a low melting point, and a spring active between said housing and said bar to urge said bar upwardly away from said; first terminal in a direction substantially perpendicular-toits length, thereby tensioning said one link section and the connection between it and said bar.

5, A fuse construction comprising a hollow housing having firstand second terminals exposed at the exterior thereof, said rst terminal being at the bottom of said housing and said second terminal being at the side thereof, apairA of link sections, one connected to said first terminal andf extending up into said housing, the other connected to said s econdterminal and extending into said housing toa point separated from the end of said one link section, .said-ione,y link section being fusible, a connecting bar of materialV having a comparatively high resistance electrically connected to the ends of said link sections and connected to theY end of said one link section by material having a low melting point, and a spring compressed between the` bottom of said housing and said bar `to urge said bar upwardly away fromV said rst terminal, thereby tensioning s aid'g one-,link section and the connection betweenit and said bar,

oi said link sections extends, and a second washer at the bottoni of said housing, said spring being compressed between the lower surface of said first washer and the upper surface of said second washer.

8. The fuse construction of claim 1, in which said bar is connected to both of said link sections by material having a low melting point.

9. The fuse construction of claim 2, in which said bar is connected to both of :said link sections by material having a low melting point.

10. The fuse construction of claim 3, in which said bar is connected to both of said link sections by material having a low melting point, said other of said link sections extending through said housing to lsaid bar in a direction substantially parallel to that of said one of said link sections and having a portion thereof spaced from said bar xed relative to said housing.

11. The fuse construction of claim 4, in which said bar' is connected to both of said link sections by material having a low melting point, said other of said link sections extending through said housing to said bar in a direction substantially parallel to that of said one of said link sections and having a portion thereof spaced from said bar fixed relative to said housing,

References Cited in the tile of this patent UNITED STATES PATENTS 1,685,958 Sandin Oct. 2, 1928 2,111,749 Bussmann Mar. 22, 1938 2,293,950 Price Aug. 25, 1942 2,563,812 Berthel Aug. 14, 1951 

